Coloration of hair is a procedure practiced from antiquity employing a variety of means. In modern times, the most extensively used method employed to color hair is to color hair by an oxidative dyeing process employing hair coloring systems utilizing one or more oxidative hair coloring agents in combination with one or more oxidizing agents.
Most commonly a peroxy oxidizing agent is used in combination with one or more oxidative hair coloring agents, generally small molecules capable of diffusing into hair and comprising one or more primary intermediates and one or more couplers. In this procedure, a peroxide material, such as hydrogen peroxide, is employed to activate the small molecules of primary intermediates so that they react with couplers to form larger sized compounds in the hair shaft to color the hair in a variety of shades and colors.
A wide variety of primary intermediates and couplers have been employed in such oxidative hair coloring systems and compositions. Among the primary intermediates employed there may be mentioned p-phenylenediamine, p-toluenediamine, p-aminophenol, 4-amino-3-methylphenol, and as couplers there may be mentioned resorcinol, 2-methylresorcinol, 3-aminophenol, and 5-amino-2-methylphenol. A majority of the shades have been produced with dyes based on p-phenylenediamine.
For providing a blue coloration to hair, m-phenylenediamine has been extensively used in combination with p-phenylenediamine as a primary intermediate. However, the blue dyes resulting undergo intramolecular cyclization to form red 2,8-diaminophenazine. This conversion has been suggested to be responsible for fading to red in hair (warm wearing or red fading). The rate of the cyclization depends upon positions of the substituents and can be decreased by the use of m-phenylenediamine with an electron-donating substituent such as an alkoxy group. Because of the color change over a period of time, there is a need for new blue couplers for use in oxidative hair dyeing compositions and systems.